I. Field of the Invention
The present invention relates generally to mechanical transfer mechanisms and, more particularly, to a lift and carry transfer mechanism with automatic accumulating means.
II. Description of the Prior Art
Conveyors and conveyor systems are currently employed in manufacturing plants and facilities for transporting parts or pieces throughout the manufacturing plant. In one type of conveyor system, the parts or workpieces are longitudinally supported along a frame defining a conveyor track by work support members spaced at predetermined intervals along the conveyor frame.
A carriage assembly is both longitudinally and vertically slidably mounted to the conveyor frame and includes a plurality of longitudinally spaced lifting members secured to the carriage assembly so that at least one lifting member is associated with each work station. In operation, as the carriage assembly is moved to its upper vertical position, the lifting members lift the workpiece off from support members at their associated work station and, upon forward longitudinal travel of the carriage assembly, carry the workpiece to the next forward work station. At the next forward work station, the carriage assembly is moved to its lower position thus placing the workpieces on the work support members at the next forward work station after which the carriage assembly is retracted and the process is then again repeated.
Conventionally, the lifting members on the carriage assembly are rigidly secured to the carriage assembly so that the parts or workpieces positioned along the conveyor track and at the work stations are incrementally moved from one work station and to the next forward work station in unison with each other. One disadvantage, however, of the lift and carry conveyor systems of this type is that a vacant space along the conveyor track caused by the absence of a workpiece at that work station will also be moved along the conveyor track in unison with the workpieces. These vacant spaces along the conveyor track, of course, are disadvantageous since the conveyor system is not used at its maximum capability. Moreover, the lack of a workpiece or part at a designated work station in predetermined intervals can cause work interruptions and even a stoppage of the entire manufacturing line.
There have, however, been previously known conveyor systems in which pusher dogs are selectively actuated or moved to an upper workpiece engaging position in dependence upon the absence of a workpiece or part at a work station. When actuated to their upper workpiece engaging position, the pusher dogs engage and slidably move a workpiece along a pair of spaced stationary rails along the conveyor track. One conveyor system of this type is disclosed in U.S. Pat. No. 3,557,943 which issued on Jan. 26, 1971, to Richard Broser.
In a pusher dog type conveyor system, however, the pusher dogs are conventionally mounted to either a conveyor frame or a carriage assembly so that the pusher dogs are pivotal between an upper workpiece engaging position and a lower workpiece clearing position. Thus, retraction of the pusher dogs from their forwardmost position and to their rearwardmost position does not undesirably cause an interference between the pusher dogs and the workpieces upon the conveyor track. Conversely, in lift and carry conveyor mechanisms it is conventional to rigidly fix the lifting members to the carriage assembly and, in many cases, the lifting members themselves are merely a formed portion of the carriage assembly. Unlike the pusher dog type conveyor systems, a lift and carry conveyor system can be constructed in this fashion since the carriage is not only longitudinally slidably mounted to the conveyor frame but is also vertically movable between an upper and lower position. Consequently, with the carriage assembly in the lower position, the lifting members which are rigidly fixed to the carriage assembly will automatically clear the workpieces on the conveyor track during the retraction of the carriage assembly from its forwardmost and to its rearwardmost travel so that a pivotal connection between the lifting members and the carriage assembly is neither required nor desired.
One inherent disadvantage of the previously known lift and carry mechanisms is that the entire carriage assembly must be repeatedly moved between both an upper and lower position and also between a forward and retracted position. Consequently, the means employed to reciprocally lift and lower the carriage assembly, typically a hydraulic power mechanism, must be sufficiently powerful to lift not only the workpieces positioned along the carriage assembly but also the carriage assembly itself. As such, the power lifting means therefore, is necessarily of an expensive construction. Moreover, as the overall length of the conveyor system increases, both the difficulty and cost of insuring that the entire carriage assembly is both raised and lowered in unison is likewise increased.